Semiconductor substrates including vias of nonuniform cross section, methods of forming and associated structures

ABSTRACT

Methods for forming a via and a conductive path are disclosed. The methods include forming a via within a wafer with cyclic etch/polymer phases, followed by an augmented etch phase. The resulting via may include a first portion having a substantially uniform cross section and a second portion in the form of a hollow ball, extending laterally further within the wafer than the first portion. Back-grinding the wafer to the second portion of the via may create a vent. A conductive path may be formed by filling the via with a conductive material, such as solder. Flux gases may escape through the vent. The wafer surrounding the second portion of the via may be removed, exposing a conductive element in the shape of a ball, the shape of the second portion of the via. Semiconductor devices including the conductive paths of the present invention are also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of semiconductordevice fabrication and, more particularly, to wafers having vias formedtherein. Methods of forming vias, including vented vias and vias filledwith conductive material and having conductive elements thereon are alsoincluded.

2. Background of Related Art

Semiconductor chips may be produced with integrated circuits on one or(less commonly) both sides of the chip and may be designed to connect toor interact with other electronic components or other semiconductorchips. Interposers may be utilized for interfacing two electricalcomponents, such as a semiconductor device and a printed circuit board,and contactor boards may be used to interface a semiconductor wafer anda probe card for testing the dice on the semiconductor wafer.Semiconductor chips may be formed of semiconductor wafer or other bulksemiconductor substrate material, while interposers and contactor boardsmay be formed of silicon, ceramic or polymeric materials.

Through-holes, or vias, which have been conductively lined or filled aretypically used for connecting an integrated circuit on one side of achip to conductive traces on the other side of the chip, a ground orother bias voltage, another electronic component or an integratedcircuit on another chip. Vias are also used for providing electricalcommunication between structures disposed on opposing sides of aninterposer or contactor board, wherein the structures may align withcontact pads or other structures of electrical components and establishelectrical connection between the various components.

Vias may be filled with conductive material in the form of solder. Thevia sidewalls may be coated with flux, such as hydrochloric acid orborax, to prevent oxides from separating the solder from the sidewalls.A solder paste, which may be as much as 50% flux, may be used to fillthe vias, then heated to reflow the solder paste. During the heatingprocess, one or more pockets of flux gases may form within the solder.Such pockets may cause the solder to expand outside the via. Solderexpanding outside the via may touch an adjacent via or other conductiveelement and, thus, create a short circuit. When the pocket of flux gasis unable to escape, a void is created. If large enough, these voids cancompromise reliability in the systems they inhabit by impairing anelectrical connection or providing a connection which may fail laterduring use. A hole may be laser-drilled to the bottom of a blind via toprovide a vent for the flux gases; however, this requires an additionalprocessing step and additional equipment.

Conventionally, preformed solder balls may be positioned over the end ofeach via, and heated to reflow and attach the solder balls to theconductive material of the via. The contact between the conductivematerial of a via and a solder ball may create a brittle solder jointline susceptible to failure. Solder bumps may be formed or placed on thevia in many ways, including evaporation, electroplating, printing,stenciling, jetting, stud bumping, and direct placement.

Accordingly, a need exists for a method of forming vias having a vent torelease solder flux gases. Being able to form solder balls on viaswithout a brittle solder joint line therebetween would also be useful.

BRIEF SUMMARY OF THE INVENTION

The present invention, in a number of exemplary embodiments, includesmethods for forming through-hole vias, which are also sometimes known as“through-wafer interconnects,” or “TWIs,” in semiconductor wafers, otherbulk semiconductor substrates, and other semiconductor componentstructures. The through-hole vias may be vented, enabling gases toescape from the vias, particularly while being filled with conductivematerial. Semiconductor component structures that include the vias andassociated structures are also within the scope of the presentinvention.

In a first exemplary method of forming a via in a semiconductor waferaccording to the present invention, a wafer having a first surface andan opposing, second surface is provided. A first via portion having afirst diameter is etched into the wafer transverse to a plane thereof toa distal, blind end by performing at least one cycle of alternatelyperforming a first etch phase and a polymer deposition phase from thefirst surface. A second via portion having a second diameter greaterthan the first diameter of the first via portion may be etched byperforming an augmented etch phase from the first surface to extend thevia deeper into the wafer from the blind end of the first via portion,the first via portion and the second via portion together forming ablind via in the wafer. A vented via may be formed by removing asacrificial portion of the wafer from the second, opposing surface to adistal tip of the blind via to provide an intermediate surface of thewafer and create a vent at the distal tip of the blind via. Theresulting vented via may be filled with conductive material, and thewafer may be etched from the intermediate surface to expose theconductive material within the second via portion of the vented via andto reach the level of a finishing surface of the wafer, the finishingsurface of the wafer opposing the first surface of the wafer. The viawithin the wafer, filled with conductive material, forms a conductivepath within the wafer. The conductive material formerly within thesecond via portion comprises a conductive element, integral with, anddisposed upon, the conductive path. A polymer collar may be formed onthe finishing surface, surrounding the exposed conductive materialadjacent the conductive path.

In another exemplary method of forming a via in a wafer according to thepresent invention, a wafer having a first surface and an opposing,second surface is provided. A first via portion having a first diameteris etched into the wafer and transverse to a plane thereof by performingat least one cycle of alternately performing a first etch phase and apolymer deposition phase from the first surface. A second via portionhaving a second diameter greater than the first diameter of the firstvia portion may be etched by performing an augmented etch phase from thefirst surface to extend the via deeper into the wafer from the distal,blind end of the first via portion. A third via portion having a thirddiameter greater than the first diameter of the first via portion may beetched by performing another augmented etch phase from the first surfacefrom the distal, blind end of the second via portion, the first viaportion, the second via portion, and the third via portion togetherforming a blind via in the wafer. A sacrificial portion of the wafer maybe removed from the second, opposing surface to a distal tip of theblind via to provide an intermediate surface of the wafer and create avent at the distal tip of the blind via, forming a vented via. Thevented via may be filled with a conductive material. A portion of thewafer and the conductive material within the second via portion and thethird via portion of the wafer may be removed to provide a finishingsurface of the wafer, the finishing surface of the wafer lying in aplane parallel to the first surface of the wafer and ending at thejuncture between the first via portion and the second via portion.

In accordance with another aspect of the present invention, asemiconductor component includes a wafer having a first surface and asecond surface opposing the first surface. The wafer includes at leastone via therein, the via having a first via portion with a substantiallyuniform cross section extending from the first surface, and a second viaportion in the form of a hollow ball positioned adjacent the first viaportion. The first via portion may have sidewalls characterized by aseries of adjacent concave scallops, while the second via portion mayhave sidewalls characterized by a single concave scallop, defining thehollow ball.

Other and further features and advantages of the present invention willbe apparent from the following descriptions of the various embodimentswhen read in conjunction with the accompanying drawings. It will beunderstood by one of ordinary skill in the art that the followingembodiments are provided for illustrative and exemplary purposes only,and that numerous combinations of the elements of the variousembodiments of the present invention are possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1E illustrate a method of forming a via in a wafer;

FIGS. 2A-2E depict an exemplary method of forming a vented via in awafer;

FIGS. 3A-3C illustrate an exemplary method of forming a conductive paththrough the wafer;

FIGS. 4A-4D illustrate another exemplary method of forming a vented viaand a conductive path in a wafer;

FIG. 5 illustrates a stacked semiconductor device assembly includingvias and conductive elements of the present invention; and

FIG. 6 is a schematic diagram of an electronic system having at leastone component incorporating vias and conductive elements of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring in general to the accompanying drawings, various aspects ofthe present invention are illustrated to show exemplary wafers includingthrough-hole vias, vias with conductive material disposed therein andconductive elements positioned thereon, as well as methods of formingvias. Common elements of the illustrated embodiments are designated withlike reference numerals for clarity. It should be understood that thefigures presented are not meant to be illustrative of actual views ofany particular portion of a particular wafer, but are merely idealizedschematic representations which are employed to more clearly and fullydepict the invention. It will be apparent by those of ordinary skill inthe art that while the methods and structures disclosed herein describemethods for fabricating vias, the acts and structures described hereincomprise a portion of an entire fabrication process of a semiconductordevice or other substrate and may be used in combination with othersemiconductor fabrication methods.

The term “wafer” used in the following description refers to anygenerally planar supporting structure including, but not limited to,semiconductor wafers, other bulk semiconductor substrates or othersemiconductor component structures. The term should be understood toinclude silicon, silicon-on-insulator (SOI), silicon-on-sapphire (SOS),doped and undoped semiconductors, epitaxial layers of silicon supportedby a base semiconductor foundation, and other semiconductor structures.A wafer may comprise primarily silicon, as formed in the art by growinga single crystal in the form of a cylinder, which is then segmented orsliced transversely to form a plurality of wafers. However, the waferneed not be silicon-based or even a semiconductor. The wafer may besilicon-germanium, germanium, gallium arsenide, indium phosphide, or asuitable ceramic or glass. When reference is made to a “wafer” in thefollowing description, previous process steps may have been utilized toform active regions or junctions in or on the wafer.

A via may be formed in, for example, a silicon wafer using a deepsilicon etch process as described hereinbelow, such as deep reactive ionetching (DRIE). One example of DRIE is the “Bosch” process, described inU.S. Pat. No. 4,855,017 to Douglas, entitled “Trench Etch Process for aSingle-Wafer RIE Dry Etch Reactor” the disclosure of which isincorporated by reference herein. FIGS. 1A-1E depict one embodiment of aDRIE method of forming a via portion 230 in a wafer 200, alternatingcycles of an etch phase and a deposition phase. FIG. 1A depicts thewafer 200. The wafer 200 may have a thickness t sufficient fordurability during handling and transport of the wafer 200. A minimumhandleable thickness for a wafer 200 is typically about 300 μm. A mask210 may be disposed on a first surface 260 of the wafer 200 and may bepatterned with at least one aperture 220 therethrough to define adesired location for the formation of a via within the wafer 200. Themask 210 may comprise either an organic-based photoresist, asilicon-based imageable masking material, or a hard mask material, suchas, by way of example and not by way of limitation, silicon oxide,silicon nitride, or silicon oxynitride. Deposition and patterning of themasking layer may be performed using techniques known in the art,depending on the particular masking material used.

FIG. 1B shows the wafer 200 after performance of a DRIE etch phase forinitial via 106 formation. The wafer 200 may be etched by exposing thewafer 200 to a plasma generated from a fluorine-containing gas. Thefluorine-containing gas may comprise at least 70 volume % of the plasmasource gas used during etching. The fluorine-containing gas may beselected from the group consisting of SF₆, CF₄, NF₃, and combinationsthereof. Sulfur hexafluoride (SF₆) is typically used in the art. Theplasma source gas may optionally include a nonreactive, diluent gas,such as, for example and not by way of limitation, argon, helium, xenon,krypton, and combinations thereof.

The etch phase may be followed by a DRIE deposition phase. FIG. 1Cdepicts a coating 108 of polymer deposited on the bottom and sidewallsof the initial via 106. The coating 108 of polymer or other suitablematerial may help prevent lateral etching of the via sidewall 105 duringa vertical etch portion of a subsequent cycle. To form the coating 108,the wafer 200 may be exposed to a plasma generated from a gas which iscapable of forming a polymer, for example, on etched silicon surfaces.The polymer-forming gas may be a carbon-containing gas, such as C₄F₈,CH₂F₂, CHF₃, or CF₄. C₄F₈ is typically used in the art. Thepolymer-forming gas may also be HBr or other compounds capable ofreacting with silicon to form a polymer. Hydrogen from the HBr may reactwith carbon from a photoresist masking layer to form an organic polymer.Alternatively, if a silicon oxide mask 210 is used, bromine from the HBrmay react with oxygen from the oxide mask 210 and silicon from thesubstrate being etched to form silicon oxybromide, a nonvolatile etchbyproduct which deposits on etched silicon surfaces.

The DRIE etch and polymer deposition phases may be repeated for a numberof cycles. FIG. 1D shows the wafer 200 after the start of a second etchphase. The bottom 110 of the initial via 106 has been cleared ofpolymer. FIG. 1E shows the wafer 200 after the completion of the secondetch phase. The process conditions used during the second (or third, orfourth, etc.) etch phase may be the same or different from those used inthe first etch phase, but typically will be similar to provide a firstvia portion 230 (FIG. 2A) having a substantially uniform cross-sectionaldiameter as the first via portion 230 extends into the wafer 200. Theplasma source power, for example, may be varied from etch phase to etchphase, or the substrate bias voltage may be varied, so that the etchprofile can be closely controlled and defined. While the via portion 230may have a substantially uniform cross-sectional diameter, the cyclingof gases in the etch/deposition process introduces a unique type ofsidewall roughness, known as scalloping.

FIG. 2A depicts the wafer 200 after several cycles of the DRIEetch/deposition process with the first via portion 230 having sidewalls235 with scallops 107. Scalloping occurs because the selected etch maybe relatively isotropic. Because of the discontinuous etch anddeposition steps in a DRIE etch/polymer deposition process, thecross-sectional etch profile of a single etch cycle when forming a viamay not exhibit a linear sidewall portion, but rather a concave sidewallportion. Every etch/deposition cycle may, thus, leave a concave scallop107 forming a portion of the first via sidewall 235. This shape is thenrepeated for each successive etch phase, resulting in a sidewall 235with a wavy, scalloped cross-sectional profile.

The first via portion 230 depicted in FIG. 2A is a blind via, i.e., avia which does not extend entirely through the wafer 200. The first viaportion 230 may be formed in the wafer 200 by multiple cycles of theDRIE cyclic etch/deposition method described hereinabove. The first viaportion 230 may be formed to the desired depth, for example, to a depthd₁ of about 150 μm into the wafer 200 having a thickness t of, forexample, about 300 μm or greater. The first via portion 230 may have adiameter d_(v) of, for example, about 50 μm.

FIG. 2B illustrates the wafer 200, wherein an augmented etch phase usingthe same type of etch (DRIE) may be used to form a second via portion, asubstantially spherical cavity 240, which may also be characterized as ahollow ball, at the base of the first via portion 230, distal from thefirst surface 260 of the wafer 200. The substantially spherical cavity240 may extend further laterally within the wafer 200 than the first viaportion 230. During the augmented etch phase, the wafer 200 may, forexample, be exposed to the etchant for an extended period of time orunder an increased pressure to increase the etch rate. The polymerdeposition phase may be postponed until the substantially sphericalcavity 240 has reached the desired dimensions; alternatively, there maybe no final polymer deposition phase employed. The substantiallyspherical cavity 240 may have a diameter d_(b) greater than the diameterd_(v) of the first via portion 230. The augmented etch cycle enables aninclusive via 150, including both the first via portion 230 and thesubstantially spherical cavity 240, to be formed in a shorter time span,and with fewer steps than required to form a via of equal depth usingthe cyclic plasma etch/polymer deposition phases used to form the firstvia portion 230. That is, the depth d₁ of the first via portion 230 plusthe depth d₂ of the substantially spherical cavity 240 are formed in ashorter time span, and with fewer steps than would be required toincrease the depth d₁ of the first via portion 230 by a depth d₂ usingcontinued cyclic plasma etch/polymer deposition phases.

The depth d₂ of the substantially spherical cavity 240 may be, forexample, between half again the depth d₁ of the first via portion 230and similar to the depth d₁ of the first via portion 230. By way ofexample, and not limitation, the depth d₂ of the substantially sphericalcavity 240 and, also, the diameter d_(b) thereof may be between about 80μm and 125 μm. It will be understood by one skilled in the art that thesubstantially spherical cavity 240 may be spherical in shape, or may besomewhat oblong on shape. Thus the depth d₂ of the substantiallyspherical cavity 240 may be greater or less than the substantiallyspherical cavity diameter d_(b). The sidewalls 246 of the substantiallyspherical cavity 240 are concave, however, because the substantiallyspherical cavity 240 is formed in a single, augmented etch phase, thesubstantially spherical cavity sidewalls 246 do not have the scallopedprofile of the sidewalls 235 of the first via portion 230.

The first via portion 230 is formed from the first surface 260 of thewafer 200 as described hereinabove. The first surface 260 is illustratedcovered with the mask 210 in FIG. 2B. After formation of the first viaportion 230 and the substantially spherical cavity 240, the mask 210 mayoptionally be removed, for example, using a chemical etch or anabrasive, mechanical method. As depicted in FIG. 2C, the first surface260 of the wafer 200 may be affixed to a wafer tape 265, also known as adicing tape. The wafer tape 265 may comprise a PVC sheet or film with anadhesive on one side to hold the wafer 200. One exemplary type of wafertape 265 is UV-tape, an adhesive tape which has sufficient adhesivestrength to secure the wafer 200 during dicing or grinding, yet theadhesive strength may diminish after being irradiated with UVirradiation. After the UV irradiation, the wafer tape 265 may be easilypeeled off from the wafer 200 in a picking-up or delamination process.

FIG. 2C depicts a sacrificial portion 250 of the wafer 200, the portionof the wafer 200 through which the first via portion 230 andsubstantially spherical cavity 240 do not extend, and including a secondsurface 270. The second surface 270 opposes the first surface 260, whichis adhered to the wafer tape 265. The sacrificial portion 250 of thewafer 200 may be removed, for example by mechanical or chemical methods,such as back-grinding, chemical mechanical planarization (CMP) or achemical wet etch to open substantially spherical cavity 240 from thesecond surface 270 and form a vented via 280, as shown in FIG. 2D. Theremoval of wafer material from the second surface 270 forms anintermediate surface 290 of the wafer 200, a surface within a planesubstantially parallel to the first surface 260, and including the tip245 of the substantially spherical cavity 240, the point farthest fromthe first via portion 230. The intermediate surface 290 may be breachedat the tip 245 of the substantially spherical cavity 240, to form a vent300. The intermediate surface 290 may be breached by the back-grindingas the wafer 200 enclosing the tip 245 of the substantially sphericalcavity 240 is removed. Optionally, the intermediate surface 290 may bebreached to form a vent 300 using a laser ablation process after thelevel of intermediate surface 290 has been reached, yet contact withsubstantially spherical cavity 240 has not been achieved; however, laserablation will require an additional process act. It will be furtherunderstood by one of ordinary skill in the art that the method presentedherein may also be used to form a via and conductive element, asdescribed hereinbelow, without breaching the intermediate surface 290 ofthe wafer 200 and forming a vent 300.

FIG. 2E depicts a close-up view of a portion of the wafer 200 and asidewall 285 of the vented via 280. The sidewall 285 of the vented via280 are covered with the coating 108, formed as described hereinaboveduring the polymer deposition phase of the deep silicon etch process bywhich the vented via 280 has been formed. The sidewall 285 may furtherbe coated with a further dielectric layer 320 and a conductive layer330. The further dielectric layer 320, also known as a passivationlayer, may comprise any known insulating material such as silicon oxide,silicon nitride or silicon oxynitride deposited to any desired thicknessusing chemical vapor deposition (CVD), pulsed laser deposition (PLD) orother known deposition process. The dielectric layer 320 may also begrown on exposed walls of the vented via 280 using an oxidizingatmosphere such as steam and oxygen at an elevated temperature. Thedielectric layer 320 may also comprise an insulating polymer, such as apolyimide deposited using a suitable process such as a spin-on processor an injection or capillary process, a Parylene™ polymer, orbenzocyclobutene (BCB). The dielectric layer 320 may provide anelectrically insulative layer of separation between the inner surface ofthe vented vias 280 and any conductive material forming a conductivepath within the vented via 280, as described hereinbelow.

A physical vapor deposition (PVD, or sputtering) process or chemicalvapor deposition (CVD) process may be used to form the conductive layer330. Alternatively, an electroless or an electrolytic plating processmay be used to form the conductive layer 330. In such instances, a seedlayer may be formed on the sidewall 285 prior to plating, as known inthe art. The conductive layer 330 may comprise a material highlywettable by most solders, for example, a metal material such as nickelor copper.

The vented via 280 may be filled with a conductive material, forexample, using a wave soldering process, as schematically depicted inFIG. 3A. Prior to filling the vented via 280, solder flux may be appliedto the wafer 200 so that during the subsequent solder fill operation,the solder will wet the conductive layer 330 (FIG. 2E) within the ventedvia 280. The flux may be sprayed into the vented via 280. The wafer 200may be transported through a wave solder machine wherein the wafer 200is moved over a wave of solder 340. The wave of solder 340 contacts thefirst surface 260 of the wafer 200 and is drawn or forced up into thevented via 280. The solder wets to the conductive layer 330 and fillsthe vented via 280. Flux gases 350 may escape through the vent 300.

Another exemplary method of filling the vented via 280 with a conductivematerial includes physically placing a solder paste into the via, forexample, by squeegeeing. Suitable solder pastes for use with the instantprocess can comprise any combination of chemical components that producepaste properties resulting in the desired chemical and physicalcharacteristics for application (e.g., bonding characteristics andviscosity), reflow, cleaning, and formation of a final, encapsulated,raised ball-bond semiconductor structure. The solder paste may be alow-melting-point alloy, usually of lead (Pb) and tin (Sn), that wets tocopper or nickel, conducts current, and mechanically joins conductorsand the like. Other suitable ingredients for use as a solder pasteinclude, without limitation, aluminum, palladium, gold, copper, indium,silver, tin, lead and combinations or alloys thereof. The solder pastemay conventionally include a blend of the desired weight percent ofalloy powder into a flux to produce a substantially homogeneous product.The wafer 200 may then be heated to reflow the solder, fill the ventedvia 280, and form a conductive path through vented via 280, anyvolatilized flux being vented, leaving a void-free conductive path.Alternatively, a solder fill process using application of preformedsolder balls to a surface of the wafer followed by heating to reflow thesolder and application of a vacuum from the opposing surface of thewafer to draw the molten solder into the via, as known in the art, maybe used.

Referring back to FIG. 2B, an inclusive via 150 including the first viaportion 230 and the substantially spherical cavity 240 may be filledwith a conductive material without breaching the intermediate surface290 of the wafer 200 and forming a vent 300. The inclusive via 150 is ablind via, and may be filled using a vacuum solder technique. Inside aclosable chamber, a flat, shallow pan with a conductive material, forexample, molten solder may be provided. The chamber atmosphere isideally purged of all oxygen using nitrogen or other inert or oxidereducing gas. The wafer 200 with inclusive via 150 may be placed in thechamber with the first surface 260 of the wafer 200 facing down towardsthe molten solder. A vacuum may be drawn, and the first surface 260 ofthe wafer 200 is then lowered into molten solder. The wafer 200 can becompletely submerged, but this is not necessary so long as the firstsurface 260 is in contact with the solder. The chamber may then bevented back to atmospheric pressure (plus or minus) to draw or force themolten solder into the inclusive via 150. The wafer 200 may be removedfrom the molten solder and cooled, leaving the solder within theinclusive via 150. The wafer 200 may be removed from the chamber andback-ground and/or etched to expose a substantially spherical conductiveelement 360 as described hereinbelow and depicted in FIG. 3C.Alternatively, the wafer 200 may be placed into the solder face up. Thewafer 200 may be completely submerged to allow solder to flow over andcompletely cover the first surface 260 of the wafer 200 prior to ventingback to atmospheric pressure to force the solder within the inclusivevia 150.

In another method for filling the inclusive via 150, a solder ball maybe applied on the first surface 260, at the top of the inclusive via 150opening. The wafer 200 may be placed into a vacuum heating chamber. Thevacuum may be drawn, and heat applied to reflow the solder. When thesolder balls become molten, the chamber may be backfilled with nitrogento approximately atmospheric pressure. Solder will then be forced intothe inclusive via 150. The solder may be cooled to solidify. The wafer200 may then be removed from the chamber and back-ground and/or etchedto expose the solder ball as described hereinbelow and depicted in FIG.3C.

The use of vacuum methods such as described hereinabove may beparticularly useful where there is no wettable metal plating such as theconductive layer 330 depicted in FIG. 2E. Plating may be eliminatedduring use of vacuum methods as the solder is forced into the viasinstead of relying upon capillary or wetting forces.

FIG. 3B depicts wafer 200 in an inverted position, the vented via 280being completely filled with conductive material 310. A substantiallyspherical conductive element 360, for example, a solder ball, has beenformed within the substantially spherical cavity 240 of the vented via280. A conductive path 370 is formed by the solder residing in the firstvia portion 230 of the vented via 280, which conductive path is integralwith the substantially spherical conductive element 360. The portion ofthe wafer 200 surrounding the conductive element 360 may be removed fromthe intermediate surface 290, for example, using a chemical etch. Oneexample of an isotropic wet etch uses a mixture of nitric acid (HNO₃)and hydrofluoric acid (HF). The nitric acid consumes the silicon surfaceto form a layer of silicon dioxide, which in turn is dissolved away bythe HF. Alternatively, the portion of the wafer 200 may be removed withCMP using a soft pad and a chemical solution highly selective tosilicon, to expose the substantially spherical conductive element 360 asdepicted in FIG. 3C. A finishing surface 390 of the wafer 200, extendinglaterally from the junction point of the substantially sphericalconductive element 360 and the conductive path 370 may thus be formed. Alayer of dielectric material may then be formed on the finishing surface390 of the wafer 200, surrounding the base 365 of the conductive element360 to form a polymer collar 380, which may improve the jointreliability between substantially spherical conductive element 360 andconductive path 370, particularly the fatigue performance thereof duringthermal cycling. The conductive element 360 may, optionally, be heatedin a reflow process, as known in the art, to reform the conductiveelement 360 in a more perfect sphere.

The conductive element 360 may be formed within the substantiallyspherical cavity 240 to be more diminutive in size than a solder ballformed by a conventional method, such as evaporation, electroplating,printing, jetting, stud bumping, and direct placement. For example, whenprinting or jetting solder to form a solder ball, a minimum quantity ofsolder must be extruded or jetted, and thus the solder ball formed mustbe at least as large as this minimum size. In contrast, the conductiveelement 360 may have a significantly smaller diameter corresponding tothe diameter d_(b) of the substantially spherical cavity 240, whichserves as mold cavity to form the substantially spherical conductiveelement 360. The substantially spherical conductive element 360 may havea diameter smaller than the diameter d_(b) of the substantiallyspherical cavity 240 because the interior of the substantially sphericalcavity 240 may be covered with the polymer coating 108, the dielectriclayer 320, and the conductive layer 330, some or all of which may beremoved by etching of wafer 200 to finishing surface 390 (see FIG. 2E).Thus, conductive elements 360 having a diameter of as little as 60 μmmay be formed once, for example, dielectric layer 320 and conductivelayer 330 have been removed from the outer surface of conductivematerial 310. Optionally, the conductive element 360 may include theconductive layer 330, if this layer is not removed with the portion ofthe wafer 200 surrounding the conductive element 360. In yet anotherapproach, only the sidewalls of the first via portion 230 may remaincovered with the conductive layer 330, and not the substantiallyspherical cavity 240. In such an instance, the wafer 200, polymercoating 108, and the dielectric layer 320 may be etched back, and theresulting conductive element 360 may be formed entirely of theconductive material 310 used to fill the vented via 280. For example,the conductive element 360 may be a solder ball. The conductive element360 of the present invention is integrally formed with the conductivepath 370 and, therefore, may have a high ball-shear strength, a measureof the reliability of a solder joint between a solder ball andconductive material, for example, conductive material within a via. Theconductive material 310 of the conductive element 360 is providedsimultaneously with the conductive material 310 filling the vented via280 and, therefore, fewer processing acts are required, compared with atypical method of forming or applying conductive elements in a separateact after the formation and filling of through-hole vias.

In a second exemplary method of forming a vented via, a first viaportion 230, as depicted in FIG. 2A, is formed within a wafer 400 to,for example, a depth _(d1) of about 150 μm, as described hereinabove. Amask 210 may be disposed over a first surface 460 of the wafer 400, asdescribed with respect to the first embodiment of the present invention.The formation of the first via portion 230 using DRIE is followed by afirst augmented etch phase, a polymer deposition phase, and a secondaugmented etch phase to form the structure depicted in FIG. 4A. Eachaugmented etch phase forms a substantially spherical cavity 440, 445,the cavities together comprising an extended via portion 410 having anincreased maximum diameter in comparison to the diameter of the firstvia portion 230. The extended via portion 410 may be positioned deeperwithin the wafer 400, farther from the first surface 460, than the firstvia portion 230. Each substantially spherical cavity 440, 445 may extendlaterally within the wafer 400 farther than the first via portion 230.In other words, the diameter of each substantially spherical cavity 440,445, may be greater than the diameter of the first via portion 230. Thefirst via portion 230 may extend within the wafer 400 to a depth d₁ ofabout 150 μm. Each substantially spherical cavity 440, 445 may extend toa depth of, for example, about 75 μm. Two scallops 403, 404, each havinga greater length d₃, d₄ in comparison to the length L of the individualscallops 401 of the first via portion 230 form a sidewall of theextended via portion 410. For example, the length L of the individualscallops 401 of the first via portion 230 may be about 1 μm, compared tothe length d₃, d₄ of the scallops 403, 404 of the substantiallyspherical cavities 440, 445, which may each be about 75 μm.

A sacrificial portion of the wafer 400, the portion of the wafer 400from a second side 470 of the wafer 400 to the level of an intermediatesurface 490 at the tip of the substantially spherical cavity 445, may beremoved, as by the previously described chemical or mechanical methods,to form the structure depicted in FIG. 4B. A vented via 480 within thewafer 400 includes a first via portion 230 having a substantiallyuniform cross-sectional diameter in communication with substantiallyspherical cavity 445 distal from the first via portion 230 whichincludes a vent 300 comprising an aperture through the exposedintermediate surface 490 of the wafer 400. Using more than one augmentedetch phase to form the vented via 480 enables a via of a desired lengthto be formed more deeply into a wafer 400 using only a few additionaletch cycles, and faster than forming a via to the desired length usingetch/deposition cycles of consistent intensity. Furthermore, using adeeper etch than in the first embodiment by performing an additionalaugmented etch cycle requires the wafer 400 to be back-ground to openthe blind end of the via only to a thickness of, for example, about 300μm rather than about 230 to 275 μm, leaving a much more robust waferstructure for filling the vented via 480 with solder.

The sidewall of vented via 480 may be coated with a dielectric layer,and plated with a conductive layer, then filled with a conductivematerial 412, for example using a solder wave machine, a vacuum/reflowmethod, or placing a solder paste within the vented via 480, followed byreflow, in the manner previously described with respect to the firstembodiment. A portion of the wafer 400 may be removed, from theintermediate surface 490 to a plane 495 within the wafer 400 includingthe junction between the first via portion 230 and the substantiallyspherical cavity 440. The removal may take place using chemical ormechanical methods, for example, wet etching or chemical mechanicalplanarization. In addition to the portion of the wafer 400 surroundingthe substantially spherical cavities 440, 445, the conductive material412 within the substantially spherical cavities 440, 445 may itself beremoved, in which instance back-grinding the wafer 400 may be the mostexpeditious approach. FIG. 4D depicts a wafer 400 having a conductivepath 370 formed therein, from the first surface 460 of the wafer 400 toa finishing surface 590 corresponding to the plane 495. It should benoted that, if conductive material 412 within substantially sphericalcavities 440, 445 is not removed by back-grinding, such conductivematerial 412 may be reflowed to produce a larger diameter solder ballthan in the case of the first embodiment, if desired.

FIG. 5 depicts a stacked assembly 500 of semiconductor components in theform of a plurality of semiconductor devices 510, mounted to a substrate520. Conductive paths 370 with integrally formed conductive elements 360connect the semiconductor devices 510 and the substrate 520. Thesubstrate 520 may include a pattern of conductive traces thereon, withwhich the conductive elements 360 may be in electrical communication.The conductive elements 360 may have a diameter d_(c) of, for example,between about 60 μm and about 100 μm. The separation or standoff of thelowermost semiconductor device 510 and the substrate 520 may, therefore,be between about 60 μm and 100 μm. The total thickness t_(a) of thestacked assembly 500 may be smaller than a stacked assembly includingconventionally formed solder balls, which may have a greater diameterthan the conductive elements 360 of the present invention. Further, thediminutive size of the conductive elements 360 enables the conductiveelements to be packed to a higher density (smaller lateral spacing, orpitch), without danger of shorting, than typical solder balls of agreater dimension.

FIG. 6 schematically illustrates an electronic system 100 including theconductive vias of the present invention. The electronic system 100includes a memory component 102, such as a static random access memory(SRAM), dynamic random access memory (DRAM), or other known memorycomponent, wherein the memory component 102 comprises a semiconductorcomponent having vias fabricated using methods of the present invention.The memory component 102 is operably connected to a microprocessor 104that may be programmed to carry out particular functions as known in theart.

Although the foregoing description contains many specifics, these shouldnot be construed as limiting the scope of the present invention, butmerely as providing illustrations of some exemplary embodiments.Similarly, other embodiments of the invention may be devised that do notdepart from the spirit or scope of the present invention. Features fromdifferent embodiments may be employed in combination. For example, avented via may be formed using a series of more than two augmented etchphases. The scope of the invention is, therefore, indicated and limitedonly by the appended claims and their legal equivalents, rather than bythe foregoing description. All additions, deletions, and modificationsto the invention, as disclosed herein, which fall within the meaning andscope of the claims, are to be embraced thereby.

1. A method of forming at least one via in a wafer, comprising:providing a wafer having a first surface and an opposing, secondsurface; etching a first via portion having a first diameter within thewafer by performing at least one cycle of alternately performing a firstetch phase and a polymer deposition phase from the first surface; andetching a second via portion to form a substantially spherical cavitywithin the wafer, the substantially spherical cavity having a seconddiameter greater than the first diameter of the first via portion byperforming an augmented etch phase, the first via portion and the secondvia portion together forming a blind via in the wafer.
 2. The method ofclaim 1, wherein performing the first etch phase comprises exposing thewafer, through a patterned masking layer defining a location of the atleast one via, to a plasma generated from a fluorine-containing gas. 3.The method of claim 2, further comprising selecting thefluorine-containing gas to be at least one of SF₆, CF₄, NF₃.
 4. Themethod of claim 2, further comprising selecting the patterned maskinglayer to comprise a photoresist.
 5. The method of claim 2, furthercomprising selecting the patterned masking layer to comprise one ofsilicon oxide, silicon nitride, and silicon oxynitride.
 6. The method ofclaim 1, wherein performing the polymer deposition phase comprisesexposing the wafer to a plasma generated from a gas which is capable offorming a polymer on an exposed surface of a material of the wafer. 7.The method of claim 6, wherein the gas is selected to be a gas whichreacts with silicon to form a polymer.
 8. The method of claim 2, whereinperforming the augmented etch phase comprises exposing the wafer,through the patterned masking layer, to a plasma generated from afluorine-containing gas for a longer time period than a time period of acycle of the first etch phase.
 9. The method of claim 2, whereinperforming the augmented etch phase comprises exposing the wafer,through the patterned masking layer, to a plasma generated from afluorine-containing gas at a higher pressure than a pressure of thefluorine-containing gas of the first etch phase.
 10. The method of claim1, wherein providing the wafer comprises providing a wafer including oneof silicon, silicon-on-insulator (SOI), silicon-on-sapphire (SOS), dopedsilicon, an epitaxial layer of silicon supported by a base semiconductorfoundation, another undoped semiconductor material other than silicon,and another doped semiconductor material other than silicon.
 11. Themethod of claim 1, wherein providing the wafer comprises providing awafer having a thickness of at least about 300 μm.
 12. The method ofclaim 11, wherein etching the first via portion comprises etching thefirst via portion to a depth of at least 150 μm using a plurality ofcycles of alternately performing the first etch phase and the polymerdeposition phase.
 13. The method of claim 11, wherein etching the secondvia portion comprises etching the second via portion to a depth of atleast 80 μm and a diameter of at least 80 μm.
 14. The method of claim 1,wherein etching the second via portion comprises etching the second viaportion in the form of a substantially spherical cavity within thewafer.
 15. The method of claim 1, further comprising removing asacrificial portion of the wafer from the opposing, second surface to adistal tip of the blind via to a level of an intermediate surface of thewafer to at least partially expose the substantially spherical cavitywithin the wafer and create an opening at the distal tip of the blindvia to form a vented via.
 16. The method of claim 15, wherein removingthe sacrificial portion comprises back-grinding.
 17. The method of claim15, wherein removing the sacrificial portion comprises at least one ofetching and chemical mechanical planarization.
 18. The method of claim15, further comprising depositing a passivation layer over sidewalls ofthe vented via.
 19. The method of claim 18, further comprisingdepositing a solder-wettable conductive layer over the passivationlayer.
 20. The method of claim 15, further comprising filling the ventedvia with a conductive material.
 21. The method of claim 20, whereinfilling the vented via with a conductive material comprises filling thevented via with a solder.
 22. The method of claim 21, further comprisingventing flux gases from the opening at the distal tip of the blind via.23. The method of claim 21, wherein filling the vented via with thesolder is effected by one of a wave soldering process, physicallyplacing a solder paste within the vented via, and reflowing preformedsolder balls placed over the vented via.
 24. The method of claim 20,further comprising etching the wafer from the intermediate surface toexpose the conductive material within the second via portion of thevented via to a level of a finishing surface of the wafer opposing thefirst surface of the wafer.
 25. The method of claim 24, furthercomprising removing a solder-wettable conductive layer from the exposedconductive material.
 26. The method of claim 24, further comprisingforming a polymer collar on the finishing surface of the wafer,surrounding the exposed conductive material adjacent a juncture betweenthe conductive material within the first via portion and the second viaportion.
 27. The method of claim 1, further comprising performinganother augmented etch phase from the first surface to form a third viaportion on an opposing side of the second via portion from the first viaportion, the third portion comprising another substantially sphericalcavity having a third diameter greater than the first diameter of thefirst via portion, the first via portion, the second via portion, andthe third via portion together forming a blind via in the wafer.
 28. Themethod of claim 27, further comprising removing a sacrificial portion ofthe wafer from the opposing, second surface to a distal tip of the blindvia to a level of an intermediate surface of the wafer and create a ventat the distal tip of the blind via, forming a vented via.
 29. The methodof claim 28, further comprising removing a portion of the wafer and aconductive material within the second via portion and the third viaportion of the wafer to a level of a finishing surface of the wafer, thefinishing surface of the wafer in a plane parallel to the first surfaceof the wafer and at a juncture between the first via portion and thesecond via portion.
 30. The method of claim 28, further comprisingremoving a portion of the wafer to a level of a finishing surface of thewafer, the finishing surface of the wafer in a plane parallel to thefirst surface of the wafer and at a juncture between the first viaportion and the second via portion.
 31. The method of claim 28, furthercomprising heating a conductive material filling the second via portionand the third via portion to a reflow temperature and permitting theheated conductive material to solidify into a ball.
 32. The method ofclaim 1, wherein performing the augmented etch phase further comprisesperforming a polymer deposition phase from the first surface.
 33. Amethod of forming at least one via in a wafer, comprising: providing awafer having a first surface and an opposing, second surface; etching afirst via portion having a first diameter within the wafer by performingat least one cycle of alternately performing a first etch phase and apolymer deposition phase from the first surface; etching a second viaportion having a second diameter greater than the first diameter of thefirst via portion by performing an augmented etch phase, the first viaportion and the second via portion together forming a blind via in thewafer; and removing a portion of the opposing, second surface of thewafer to at least partially expose the second via portion cavity forminga vented via in the wafer.
 34. The method of claim 33, whereinperforming the augmented etch phase further comprises performing apolymer deposition phase from the first surface.
 35. The method of claim33, further comprising filling the vented via with solder by one of awave soldering process, physically placing a solder paste within thevented via, and reflowing preformed solder balls placed over the ventedvia.